[Docs] [txt|pdf|xml|html] [Tracker] [WG] [Email] [Nits]

Versions: 00 01 02 03 04 05 06 07 08 09 10

Network Working Group                                              X. Xu
Internet-Draft                                                     K. Bi
Intended status: Standards Track                                  Huawei
Expires: June 27, 2017                                 December 24, 2016


                       BGP Neighbor Autodiscovery
                 draft-xu-idr-neighbor-autodiscovery-00

Abstract

   BGP has been used as an underlay routing protocol in many hyper-scale
   data centers.  This document proposes a BGP neighbor autodiscovery
   mechanism which can be used to simplify the BGP deployment greatly.
   This mechanism is very useful for those hyper-scale data centers
   where BGP is used as an underlay routing protocol.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on June 27, 2017.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.



Xu & Bi                   Expires June 27, 2017                 [Page 1]


Internet-Draft                                             December 2016


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  BGP Hello Message Format  . . . . . . . . . . . . . . . . . .   3
   4.  Hello Message Procedure . . . . . . . . . . . . . . . . . . .   5
   5.  HELLO Message Error Handling  . . . . . . . . . . . . . . . .   6
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   BGP has been used as an underlay routing protocol instead of IGP in
   many hyper-scale data centers [RFC7938].  Furthermore, there is an
   attempt to leverages BGP Link-State distribution and the Shortest
   Path First algorithm similar to Internal Gateway Protocols (IGPs)
   such as OSPF [I-D.keyupate-idr-bgp-spf].  In a word, there is a
   strong motivation to replace IGP by BGP in hyper-scale data centers.

   However, BGP is not good as IGP from the perspective of deployment
   automation and simplicity.  For instance, the IP address and
   Autonomous System Number (ASN) of each BGP neighbor have to be
   manually configured on BGP routers although these BGP peers are
   directly connected.  In addition, for those directly connected BGP
   routers, it's usually not ideal to establish BGP sessions over their
   directly connected interface addresses due to the following reasons:
   1) it's not convient to do trouble-shooting; 2) the BGP update volume
   is unnecessarily increased when there are multiple physical links
   between them and those links couldn't be configured as a Link
   Aggregtion Group (LAG) due to whatever reason (e.g., diffferent link
   type or speed).  As a result, it's more common that loopback
   interface addresses of those directly connected BGP peers are used
   for BGP session establishment.  To make those loopback addresses of
   directly connected BGP peers reachable from one another, either
   static routes have to be configured or some kind of IGP has to be
   enabled.  The former is not good from the automation perspective
   while the latter is in conflict with the original intention of using
   BGP as IGP.

   This draft specifies a BGP neighbor autodiscovery mechanism by
   borrowing some ideas from the Label Distribution Protocol (LDP)
   [RFC5036] . More specifically, directly connected BGP routers could



Xu & Bi                   Expires June 27, 2017                 [Page 2]


Internet-Draft                                             December 2016


   automatically discovery the loopback address and the ASN of one other
   through the exchange of the to-be-defined BGP HELLO messages.  The
   BGP session establishment process as defined in [RFC4271] is
   triggered once directly connected BGP neighbors are discovered from
   one another.  Note that the BGP session should be established over
   the discovered loopback address of the BGP neighbor.  In addition, to
   elimnate the need of configing static routes or enabling IGP for the
   loopback addresses, a certain type of routes towards the BGP
   neighbor's loopback addresses are dymatically created once the BGP
   neighbor has been discovered.  The administritive distance of such
   type of routes MUST be smaller than their equivalents which are
   learnt via the normal BGP update messages . Otherwise, circular
   dependency problem would occur once these loopback addresses are
   advertised via the normal BGP update messages as well.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  Terminology

   This memo makes use of the terms defined in [RFC4271].

3.  BGP Hello Message Format

   To automatically discover directly connected BGP neighbors, a BGP
   router periodically sends BGP HELLO messages out those interfaces on
   which BGP neighbor autodiscovery are enabled.  The BGP HELLO message
   is a new BGP message which has the same fixed-size BGP header as the
   exiting BGP messages.  However, the HELLO message MUST sent as UDP
   packets addressed to the to-be-assigned BGP discovery port (179 is
   the suggested port value) for the "all routers on this subnet" group
   multicast address (i.e., 224.0.0.2 in the IPv4 case and FF02::2 in
   the IPv6 case.  The IP source address is set to the address of the
   interface over which the message is sent out.

   In addition to the fixed-size BGP header, the HELLO message contains
   the following fields:











Xu & Bi                   Expires June 27, 2017                 [Page 3]


Internet-Draft                                             December 2016


        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     Version   |   Hold Time   |      Message Length           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                             TLVs                              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                         Figure 1: BGP Hello Message

      Version: This 1-octet unsigned integer indicates the protocol
      version number of the message.  The current BGP version number is
      4.

      Hold Time: Hello hold timer in seconds.  Hello Hold Time specifies
      the time the sending BGP peer will maintain its record of Hellos
      from the receiving BGP peer without receipt of another Hello.  A
      pair of BGP peers negotiates the hold times they use for Hellos
      from each other.  Each proposes a hold time.  The hold time used
      is the minimum of the hold times proposed in their Hellos.  A
      value of 0 means use the default 15 seconds.

      Message Length: This 2-octet unsigned integer specifies the length
      in octects of the ASN TLV, Connection Address TLV and other TLVs.

      TLVs: This field contains ASN TLV, Connection Address TLV and
      other TLVs.

   The ASN TLV format is show as follows:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |          Type=TBD2            |      Length                   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |             AS Number (2-octet or 4-octet)                    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                    Figure 2: ASN TLV

      Type: TBD2.

      Length: Specifies the length of the Value field in octets.

      AS Number: This variable-length field indicates the 2-octet or
      4-octet ASN of the sender.

   The Connection Address TLV format is shown as follows:





Xu & Bi                   Expires June 27, 2017                 [Page 4]


Internet-Draft                                             December 2016


        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |          Type=TBD3            |      Length                   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |      Connection Address (4-octet or 16-octet)                 |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                    Figure 3: Connection Address TLV

      Type: TBD3

      Length:Specifies the length of the Value field in octets.

      Connection Address: This variable-length field indicates the IPv4
      or IPv6 loopback address which is used for establishing BGP
      sessions.

4.  Hello Message Procedure

   A BGP peer receiving Hellos from another peer maintains a Hello
   adjacency corresponding to the Hellos.  The peer maintains a hold
   timer with the Hello adjacency, which it restarts whenever it
   receives a Hello that matches the Hello adjacency.  If the hold timer
   for a Hello adjacency expires the peer discards the Hello adjacency.

   We recommend that the interval between Hello transmissions be at most
   one third of the Hello hold time.

   A BGP session with a peer has one or more Hello adjacencies.

   A BGP session has multiple Hello adjacencies when a pair of BGP peers
   is connected by multiple links that have the same connection address;
   for example, multiple PPP links between a pair of routers.  In this
   situation, the Hellos a BGP peer sends on each such link carry the
   same Connection Address.  In addition, to elimnate the need of
   configing static routes or enabling IGP for the loopback addresses, a
   certain type of routes towards the BGP neighbor's loopback addresses
   (e.g., carried in the Connection Address TLV) are dymatically created
   once the BGP neighbor has been discovered.  The administritive
   distance of such type of routes MUST be smaller than their
   equivalents which are learnt via the normal BGP update messages.
   Otherwise, circular dependency problem would occur once these
   loopback addresses are advertised via the normal BGP update messages
   as well.

   BGP uses the regular receipt of BGP Discovery Hellos to indicate a
   peer's intent to keep BGP session identified by the Hello.  A BGP
   peer maintains a hold timer with each Hello adjacency that it



Xu & Bi                   Expires June 27, 2017                 [Page 5]


Internet-Draft                                             December 2016


   restarts when it receives a Hello that matches the adjacency.  If the
   timer expires without receipt of a matching Hello from the peer, BGP
   concludes that the peer no longer wishes to keep BGP session for that
   link or that the peer has failed.  The BGP peer then deletes the
   Hello adjacency.  When the last Hello adjacency for an BGP session is
   deleted, the BGP peer terminates the BGP session by sending a
   Notification message and closing the transport connection.

5.  HELLO Message Error Handling

   TBD

6.  Acknowledgements

   The authors would like to thank

7.  IANA Considerations

   TBD.

8.  Security Considerations

   TBD

9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271,
              DOI 10.17487/RFC4271, January 2006,
              <http://www.rfc-editor.org/info/rfc4271>.

9.2.  Informative References

   [I-D.keyupate-idr-bgp-spf]
              Patel, K., Lindem, A., Zandi, S., and G. Velde, "Shortest
              Path Routing Extensions for BGP Protocol", draft-keyupate-
              idr-bgp-spf-02 (work in progress), December 2016.

   [RFC5036]  Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed.,
              "LDP Specification", RFC 5036, DOI 10.17487/RFC5036,
              October 2007, <http://www.rfc-editor.org/info/rfc5036>.



Xu & Bi                   Expires June 27, 2017                 [Page 6]


Internet-Draft                                             December 2016


   [RFC7938]  Lapukhov, P., Premji, A., and J. Mitchell, Ed., "Use of
              BGP for Routing in Large-Scale Data Centers", RFC 7938,
              DOI 10.17487/RFC7938, August 2016,
              <http://www.rfc-editor.org/info/rfc7938>.

Authors' Addresses

   Xiaohu Xu
   Huawei

   Email: xuxiaohu@huawei.com


   Kunyang Bi
   Huawei

   Email: bikunyang@huawei.com


































Xu & Bi                   Expires June 27, 2017                 [Page 7]


Html markup produced by rfcmarkup 1.128b, available from https://tools.ietf.org/tools/rfcmarkup/